JP7808932B2 - Holding pad - Google Patents

Description

The present invention relates to a holding pad for polishing optical materials, semiconductor wafers, semiconductor devices, hard disk substrates, and metal and ceramic surfaces. In particular, it relates to a holding pad for polishing difficult-to-cut materials such as SiC substrates (silicon carbide wafers), GaAs (gallium arsenide) substrates, and sapphire glass.

Chemical mechanical polishing (CMP) is a commonly used polishing method for planarizing the surfaces of optical materials, semiconductor wafers, semiconductor devices, hard disk substrates, metals, ceramics, etc.

A typical CMP method will be explained using Figure 1. As shown in Figure 1, in a polishing apparatus 1 that performs the CMP method, a polishing pad 5 (which has a polishing layer) provided on a lower platen 6 and a holding pad 3 provided on an upper platen 4 rotate and press against an object to be polished 2, thereby polishing the surface of the object to be polished 2 that is in contact with the polishing surface 5A of the polishing layer. As shown in Figure 1, polishing is performed on the polishing layer in the presence of slurry S, which is supplied from a slurry supply unit 7.

Incidentally, the polishing industry as a whole is seeking highly durable holding pads that can withstand harsher polishing conditions (such as high polishing pressures and the use of highly acidic slurries) in order to improve polishing efficiency, and highly durable holding pads are particularly desired when the workpiece being polished is a difficult-to-cut material such as SiC.

Conventional holding pads include the wet film-formation type described in Patent Document 1, but the structure of wet film-formation type holding pads is destroyed in just a few hours under harsh conditions, or the structure of the holding surface is destroyed when the polished object is peeled off the holding surface after polishing, and they do not have sufficient durability.
Examples of holding pads that are less susceptible to structural damage include holding pads made of molded hard polyurethane, as described in Patent Document 2. However, if the density is low for the purpose of cushioning, slurry erodes into the voids, resulting in a loss of durability. Furthermore, under high polishing pressure conditions, the waviness of the holding pad itself is easily transferred to the workpiece. To mitigate this, the holding pad must have sufficient adhesive force in the shear direction to allow the workpiece to rotate during polishing. However, with low-density holding pads with openings larger than a certain size on the holding surface, the unevenness of the openings creates high frictional resistance in the shear direction, preventing the workpiece from rotating smoothly and lacking sufficient adhesive force to the workpiece. On the other hand, if the pad is made high-density, the pad becomes hard, resulting in poor cushioning and the risk of damaging the workpiece upon contact.

Materials other than urethane, such as polyesters like PET, can be used for the holding pad to improve chemical resistance. However, fiber-based holding pads, such as those made of nonwoven fabrics or woven fabrics as described in Patent Document 3, leave room for improvement in terms of physical durability, especially under high polishing pressure conditions. Furthermore, shed fiber fragments can cause scratches.

Patent No. 5976623 Patent No. 6757156 JP 2009-88456 A

As such, no conventional retention pads met all of the requirements of high durability, high adsorption (high retention), and chemical resistance.

As a result of extensive research, the inventors discovered that by using polyester with a void structure that meets certain requirements, it is possible to achieve higher durability and chemical resistance than urethane-based holding pads, and also to solve the problem of adsorption (retention), and thus came up with the holding pad of the present invention.
[1] A support pad including a support layer including polyester,
The density of the support layer is 0.2 to 0.6 g/cm ³ ;
A holding pad, wherein the total area ratio of openings having a diameter of 20 μm or more on the holding surface of the holding layer is 1% or less.
[2] The holding pad according to [1], wherein the polyester is polyethylene terephthalate.
[3] The holding pad according to [1] or [2], wherein the holding layer is made of a foamed polyester sheet.
[4] The holding pad according to any one of [1] to [3], wherein the total area ratio of pores equivalent to a diameter of 20 μm or more in the cross section of the holding layer is 1% or less.
[5] The holding pad according to any one of [1] to [4], wherein the holding layer has a Shore D hardness of 20 to 50 degrees.
[6] The holding pad according to any one of [1] to [5], wherein the compressibility of the holding layer is 0.1 to 3.0%.
[7] The support pad according to any one of [1] to [6], wherein the support layer is non-fibrous.

The holding pad of the present invention fully satisfies the requirements of high durability, high adsorption (high retention), and chemical resistance. Furthermore, it also has high breaking strength and low friction with the workpiece. Therefore, while maintaining adsorption, the workpiece easily rotates during polishing, enabling the workpiece to be polished uniformly.

FIG. 1 is a schematic diagram of a polishing apparatus 1.

The following describes a mode for carrying out the invention, but the present invention is not limited to this mode for carrying out the invention.

<Holding pad>
The holding pad 3 of the present invention is a holding pad including a holding layer containing polyester, wherein the density of the holding layer is 0.2 to 0.6 g/ ^cm3 , and the total area ratio of openings equivalent to a diameter of 20 μm or larger on the holding surface of the holding layer is 1% or less. Here, the total area ratio of openings equivalent to a diameter of 20 μm or larger on the holding surface of the holding layer refers to the proportion of the total area of openings equivalent to a diameter of 20 μm or larger to the total area of the holding surface.

As shown in Figure 1, the holding pad 3 is provided on the upper surface plate 4 and includes at least a holding layer. In addition to the holding layer, the holding pad 3 can also include an adhesive layer (not shown) for adhering it to the upper surface plate 4, as well as a cushioning layer, but Figure 1 only shows the holding layer of the holding pad 3, and the other layers are omitted.

<Retention layer>
The retaining layer is the layer of the retaining pad 3 that comes into contact with the workpiece 2. The material of the retaining layer contains polyester as an essential component. Examples of polyesters that can be used include PET (polyethylene terephthalate), polyethylene naphthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polypropylene terephthalate, with PET being preferred in the present invention. Note that, as long as the effects of the present invention are not impaired, the material of the retaining layer may be a mixture of resins other than polyester, such as polyurethane and epoxy resin. The preferred proportion of materials other than polyester relative to the total mass of the retaining layer is, in this order, 30% or less, 20% or less, 10% or less, and 5% or less.

Additives can be added to the polyester used as the material for the retaining layer. Additives can be used within the scope of the present invention, and examples include light stabilizers, antioxidants, water repellents, hydrophilic agents, and dyes. These additives can be used alone or in combination of two or more.

Among polyesters, polyethylene terephthalate is particularly preferred from the standpoint of processability and chemical resistance. Polyesters are generally easy to form into the desired shape and size depending on the polishing conditions, such as the polishing equipment and the workpiece, and are resistant to deterioration even when exposed to acidic or basic slurries, tending to have a long product life; this tendency is even stronger for polyethylene terephthalate.

(Density and pore size)
The retention layer has a density of 0.2 to 0.6 g/ ^cm3 , and the total area ratio of pores equivalent to a diameter of 20 μm or more on the retention surface of the retention layer (the surface in contact with the workpiece 2, 3A in FIG. 1) is 1% or less. The density (true density) of ordinary polyester without pores generally exceeds 1.2 g/ ^cm3 , but the density of the polyester used as the material for the retention layer of the present invention is 0.2 to 0.6 g/ ^cm3 . Therefore, the retention layer contains voids such as air bubbles.
In consideration of cushioning properties, the density is preferably 0.2 to 0.5 g/cm ³ , and more preferably 0.2 to 0.4 g/cm ³ .

The total area ratio of openings of 20 μm or larger in diameter on the holding surface 3A of the holding layer is 1% or less. This indicates that the holding surface is smooth and has very few openings of 20 μm or larger in diameter, but considering that the density is 0.2 to 0.6 g/ ^cm3 , this means that the holding surface contains a certain amount of very small openings. "Openings of 20 μm or larger in diameter" includes not only "circular openings of 20 μm or larger in diameter" but also "polygonal or elliptical openings having the same area as a circle of 20 μm in diameter."

In the present invention, the pores on the holding surface, i.e., the surface that comes into contact with the workpiece 2, are specified, but it is preferable that the total area ratio of pores with a diameter of 20 μm or more is 1% or less not only on the holding surface 3A but also on the cross section (i.e., the interior) when the holding layer is cut. This indicates that the holding layer as a whole has very few bubbles with a diameter of 20 μm or more, but considering that the density is 0.2 to 0.6 g/ ^cm3 , it means that it contains a certain amount of very small bubbles.

The retaining layer is preferably non-fibrous. "Non-fibrous" here means that the retaining layer material contains fibrous components such as fibers and nonwoven fabrics in an amount of 10% by mass or less relative to the total mass. It is more preferable for the retaining layer to contain fibrous components in an amount of 5% by mass or less, even more preferably 1% by mass or less, and it is particularly preferable for the retaining layer to contain no fibrous components at all (except in cases where impurities are inevitably mixed in).

The retention layer has a density of 0.2 to 0.6 g/ ^cm3 , and the total area ratio of pores equivalent to 20 μm or more on the retention surface of the retention layer is 1% or less. This prevents the slurry used during polishing from penetrating into the retention layer, thereby preventing deterioration of the retention layer. The presence of many small pores on the retention surface maintains the retention force of the workpiece 2. Furthermore, since the retention surface is not too smooth, it does not excessively adhere to the workpiece 2, suppressing the effects of unevenness caused by air bubbles, and allowing the workpiece to be polished while rotating. Furthermore, it is preferable that the total area ratio of pores equivalent to 20 μm or more in diameter is 1% or less not only on the retention surface 3A but also on the cross section of the retention layer when cut. Since the air bubbles contained in the retention layer are sufficiently fine, the retention layer holding the workpiece sinks evenly during polishing, improving flatness (polishing accuracy). The support layer of the present invention is highly suitable for use with hard-to-cut materials such as SiC substrates (silicon carbide wafers), GaAs (gallium arsenide) substrates, and sapphire glass.

(Shore D hardness)
The Shore D hardness of the retaining layer is not particularly limited, but is preferably 20 to 50. If the hardness is within 50 degrees, damage to the polished object 2 is suppressed, and if it is 20 degrees or more, durability is likely to be high.

(Compression rate)
The compressibility of the support layer is herein an indication of the softness of the support layer.
Considering cushioning properties and durability, 0.1 to 3.0% is preferable, and 0.1 to 2.0% is more preferable. Although this is particularly noticeable under high polishing pressure conditions, 0.1 to 1.5% is particularly preferable from the viewpoint of preventing the workpiece 2 from sinking into the holding pad 3 and reducing flatness. The Shore D hardness and compressibility can be adjusted by the density (porosity), etc.

The holding pad 3 shown in Figure 1 preferably has a frame material 8 on the holding surface to prevent the workpiece from falling off. Any conventionally known frame material 8 can be used, and for example, it can be made of glass fiber reinforced epoxy resin. In this specification, the holding pad 3 with the frame material 8 is referred to as a holder.

The holding pad 3 may be provided with a fixing means (not shown) on the surface opposite the holding surface 3A of the holding layer for fixing to the upper surface plate 4. Any known fixing means can be used, such as double-sided tape or adhesive.

(Polishing Layer and Polishing Pad)
The polishing pad 5 used when the holding pad 3 of the present invention is used for polishing is not particularly limited.
The polishing layer of the polishing pad 5 (the layer that comes into contact with the workpiece 2, not shown) can be suitably made of polyurethane resin, polyurea resin, or polyurethane-polyurea resin.
The thickness of the polishing layer can be generally about 1 to 5 mm, and hollow microspheres can be contained as needed.

(Cushion layer)
The polishing pad 3 may have a cushion layer (not shown) between the polishing layer and the lower platen for the purpose of more uniform contact of the polishing layer with the workpiece 2. In the present invention, any known cushion layer can be used. The cushion layer 6 may be made of any of a resin-impregnated nonwoven fabric, a flexible material such as synthetic resin or rubber, or a foam with a cellular structure. A cushion layer made of polyurethane resin with sponge-like fine bubbles is also preferably used.

(Adhesive layer)
The adhesive layer is a layer for adhering the cushion layer and the polishing layer, and is usually made of double-sided tape or adhesive, and any known adhesive layer can be used when using the holding pad 3 of the present invention. As the adhesive layer, any known double-sided tape or adhesive in the art (for example, an adhesive sheet) can be used.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples. In each example and comparative example, "parts" means "parts by mass" unless otherwise specified.

Example 1
A retainer including the retaining pad of Example 1 was manufactured using a foamed PET sheet (polyethylene terephthalate sheet) manufactured by Furukawa Electric Co., Ltd. (trade name "MCPET M4") as the retaining layer, a glass fiber reinforced epoxy resin (Gala-Epo) attached as a frame material at predetermined positions on the retaining surface, and double-sided tape attached to the surface opposite the retaining surface. In the retaining layer of the retaining pad of Example 1, no openings equivalent to a bubble diameter of 20 μm or more were observed on either the retaining surface or cross section, resulting in an open area ratio of 0%. The open area ratio was determined by observing an approximately 1.3 mm square area of the target surface under a microscope at 175x magnification, and binarizing the resulting image using image processing software (Nikon Corporation, trade name "ImageAnalyzer V20 LAB Ver. 1.3") to determine the circle-equivalent diameter and the area ratio of open holes per unit area from the area of each bubble. The specific characteristics of the retaining pad of Example 1 are shown in Table 1.

(Comparative Example 1)
A retainer including a retaining pad of Comparative Example 1 was produced in the same manner as in Example 1, except that the retaining layer was a molded type polyurethane resin with a density of 0.75 g/ ^cm3 . The properties of the retaining pad of Comparative Example 1 are shown in Table 1. The open area ratio of the retaining pad of Comparative Example 1 was the same on both the retaining surface and cross section.

(Comparative Example 2)
A holder including a holding pad of Comparative Example 2 was produced in the same manner as in Example 1, except that a molded polyurethane resin with a lower density (density 0.39 g/cm ³ ) than that of Comparative Example 1 was used as the holding layer. The properties of the holding pad of Comparative Example 2 are shown in Table 1. The open area ratio of the holding pad of Comparative Example 2 was the same on both the holding surface and cross section.

(Chemical resistance test)
A sample piece of the material used for each support pad was immersed in a hydrochloric acid solution of pH 2 for 48 hours at 40 ° C., and then a tensile test was performed to measure the tensile strength. Here, the n number for the break strength was 2, and the elongation during tension was measured using a Tensilon universal testing machine RTC manufactured by A&D Co., Ltd. in accordance with the Japanese Industrial Standards (JIS K6550). Specifically, a dumbbell-shaped measurement sample (length 90 mm, end width 20 mm, sample width 10 mm) was punched out from the support layer, and the measurement sample was clamped between the upper and lower air chucks of the measuring machine. Measurement was started at a tensile speed of 100 mm/min and an initial gripping distance of 50 mm. The break strength was calculated from the value at which the measured value reached its peak (break).

(density measurement)
The density (g/cm ³ ) of the support layer was measured in accordance with Japanese Industrial Standards (JIS K 6505).

(D hardness measurement)
The D hardness of the support layer was measured using a D-type hardness tester in accordance with Japanese Industrial Standards (JIS-K-6253). Here, the measurement sample was obtained by stacking multiple support layers as necessary so that the total thickness was at least 4.5 mm.

(Compression ratio measurement)
The compressibility can be determined using a Schopper-type thickness measuring instrument (pressure surface: circular with a diameter of 1 cm) in accordance with Japanese Industrial Standards (JIS L 1021). Specifically, the compressibility is determined as follows.
The thickness t0 was measured after applying an initial load for 30 seconds from an unloaded state, and then the thickness t1 was measured after applying a final load for 5 minutes from the thickness t0 state. The compression ratio was calculated using the formula: compression ratio (%) = 100 × ( _t0 - _t1 )/ _t0 (note that the initial load was 100 g/ ^cm2 and the final load was 1120 g/ ^cm2 ).

(Polishing performance evaluation)
Using the holders equipped with the obtained holding pads of Example 1 and Comparative Examples 1 and 2, silicon wafers were polished under the following polishing conditions.

(polishing conditions)
The conditions other than the holding pad in the abrasion test are as follows:
Grinding machine used: GRIND-X PNX332B (manufactured by Okamoto Machine Tools Manufacturing Co., Ltd.)
Polishing agent temperature: 22°C
Polishing platen rotation speed: 40 rpm
Polishing head rotation speed: 41 rpm
Polishing pressure: (external pressure) 0.016 MPa (internal pressure) 0.012 MPa
Polishing slurry: GLANZOX 1306 (20-fold dilution), GLANZOX 3105 (30-fold dilution), GLANZOX 3111 (20-fold dilution) (manufactured by Fujimi Corporation)
Polishing slurry flow rate: 800 to 1500 ml/min Polishing time: 6 to 10 minutes Polished object: silicon wafer

(Adsorption force measurement)
The holding surface of the holding pad was sprayed with water about five times with a spray bottle to moisten it for 15 minutes, and then water droplets on the surface were removed. A 4-inch silicon wafer was placed on top of the pad, and a 12 kg weight was placed on top of it for 1 minute, after which the weight was removed. Finally, the maximum force applied when the silicon wafer was lifted was measured. The measurement device used was a Tensilon Universal Testing Machine RTC manufactured by A&D Co., Ltd.

(frictional force measurement)
A 10 cm square piece of glass was used as the friction target. The holding pad was left to wet for 15 minutes before measurement. The pad was sprayed with water about five times with a spray bottle to remove the moisture, and the square glass was placed on top of it. A 10 kg weight was placed on top of it and pulled 8 cm to observe the static and dynamic friction forces.

The holding pad of Example 1, made of PET with substantially no 20 μm-equivalent voids and maintaining a low density, exhibited higher chemical resistance (breaking strength) than the holding pad of Comparative Example 2, made of polyurethane with comparable density and cushioning (D hardness). Furthermore, the holding pad of Example 1, which does not have 20 μm-equivalent pores on its holding surface, had a moderately smooth surface and therefore low frictional force. On the other hand, Comparative Examples 1 and 2, which have a predetermined adsorption force but also certain pores, exhibited higher frictional force than the holding pad of Example 1. This suggests that the holding pad of Example 1 is able to adequately adsorb and hold the workpiece to prevent it from falling off, while maintaining the workpiece in a state that allows it to rotate easily during polishing, thereby enabling uniform polishing of the workpiece. In actual polishing performance evaluations, it was confirmed that when the holding pad of the Example was used, the workpiece did not fall off during polishing, and the structure of the holding surface was not destroyed even when the workpiece was removed at the end of polishing.

This invention contributes to the manufacture and sale of polishing pads and has industrial applicability.

1 Polishing device 2 Object to be polished 3 Holding pad (holding layer)
3A Holding surface 4 Upper surface plate 5 Polishing pad 6 Lower surface plate 7 Slurry supply device 8 Frame material S Slurry

Claims (7)

A support pad comprising a support layer containing more than 70% by mass of foamed polyester relative to the total mass of the support layer,
The density of the support layer is 0.2 to 0.6 g/cm ³ ;
The support surface of the support layer has openings with a diameter of less than 20 μm,
A holding pad, wherein the holding surface of the holding layer has a total area ratio of openings with diameters of 20 μm or more of 1% or less relative to the total area of the holding surface. The support pad of claim 1, wherein the polyester is polyethylene terephthalate. The support pad according to claim 1 or 2, wherein the support layer is made of a foamed polyester sheet. A holding pad according to any one of claims 1 to 3, wherein the total area ratio of pores with a diameter of 20 μm or larger in the cross section of the holding layer is 1% or less. A support pad according to any one of claims 1 to 4, wherein the support layer has a Shore D hardness of 20 to 50 degrees. The support pad according to any one of claims 1 to 5, wherein the compression ratio of the support layer is 0.1 to 3.0%. 7. The support pad according to claim 1, wherein the content of fiber components in the support layer is 10% by mass or less relative to the total mass of the support layer .